This invention relates to alkyd resins and further relates to so-called oil-free alkyd resins which are understood to be resins which are modified with long-chain epoxides incorporated through the polybasic carboxylic acid components. More particularly, the present invention relates to oil-free alkyd resins for use in lacquers, particularly water lacquers.
It is well known that fatty acids in alkyd resins can be replaced by long-chain epoxides which are incorporated through the polybasic carboxylic acid component. Thus, U.S. Pat. No. 4,125,521 describes alkyd resins which contain as their characteristic constituent long-chain epoxy alkanes containing an internal epoxide group. These resins are suitable for use in solvent lacquers, but not in water lacquers. The claimed advantage is the increase in resistance to hydrolysis.
Oil-free alkyd resins are known in the field of water lacquers. Thus, U.S. Pat. No. 4,200,560 describes resins having an acid number of from 25 to 80 and an --OH number of up to about 180 mg of KOH/g. The claimed advantages include better weather resistance and less yellowing.
However, the usefulness of these resins is limited by the fact that it is possible to obtain films of only moderate hardness from the water lacquers thus produced. Despite their favorable weathering behavior, resins of this type are unsuitable for many external applications, including for example finish-lacquering in the automotive industry.
There is still a need for resins for water lacquers having as low an acid number as possible (for example &lt;35 or &lt;25 mg of KOH/g) because resins such as these require smaller quantities of amine for neutralization. With acid numbers as low as these, however, the resins described hitherto cannot be made up into homogeneous, clear aqueous preparations.
Accordingly, there is need to provide alkyd resins which can be stoved to form hard and flexible lacquers and which show excellent weathering behavior, particularly with respect to high resistance to water in the condensed-moisture test.